Known converter circuits are used in a large number of applications today. FIG. 1 shows a known converter circuit having a capacitive energy storage circuit 2 which has at least one capacitive energy store. Furthermore, the converter circuit has a converter unit 1, the DC voltage side of which is connected to the capacitive energy storage circuit 2. By way of example, such a converter unit is used for supplying power to an electrical load which can call for an AC voltage, for example. The converter unit 1 itself can have a multiplicity of actuatable power semiconductor switches which are connected up to form known circuits, such as half-bridge or full-bridge circuits.
Furthermore, the capacitive energy storage circuit 2 additionally can include at least one snubber network 3 (known as a snubber circuit) in order to keep down spurious high-frequency or voltage peaks on the actuatable power semiconductor switches of the converter unit 1, which can arise when the actuatable power semiconductor switches switch. Accordingly, such a snubber network 3 prompts limiting of the rate of current or voltage rise on the actuatable power semiconductor switches of the converter unit 1, such as thyristors, IGBTs, IGCTs and the like. As shown in FIG. 1, the snubber network can include a resistor, an inductance, a capacitance and a diode, being connected in the manner as shown in FIG. 1.
If an overcurrent (iF) occurs, as a result of an error in the converter unit 1, the at least one capacitive energy store and the capacitance of the snubber network 3 together with the inductance of the snubber network 3 are thus a resonant circuit which results in the overcurrent iF oscillating with a large amplitude and subsiding only slowly. Such an oscillation is shown by way of example in FIG. 2 in the waveform of the overcurrent iF. This type of oscillation in the overcurrent iF can damage or even destroy the actuatable power semiconductor switches of the converter unit 1, however, and is accordingly highly undesirable.
EP 1 619 785 A2 specifies a converter circuit of the type in question which has a snubber network with a resistor, an inductance, a capacitance and with a diode. There is no provision for a device for damping the aforementioned oscillation in an overcurrent that occurs.